package com.zhouhong.muke_leetcode;

/**
 * @ClassName: Algorithm-and-Data-Structure
 * @Description:
 * @Author: zhouhong
 * @Create: 2021-04-03 23:39
 **/
//将两个升序链表合并为一个新的 升序 链表并返回。新链表是通过拼接给定的两个链表的所有节点组成的。

public class LeetCode0021 {

    // 方法一：暴力解决
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        ListNode pre = new ListNode();
        ListNode cur = pre;
        while (l1 != null && l2 != null){
            if (l1.val <= l2.val){
                cur.next = l1;
                l1 = l1.next;
            }else {
                cur.next = l2;
                l2 = l2.next;
            }
            cur = cur.next;
        }
        if (l1 != null){
            cur.next = l1;
        }
        if (l2 != null){
            cur.next = l2;
        }
        return pre.next;
    }

    // 使用递归的方法解决
    public ListNode mergeTwoLists1(ListNode l1, ListNode l2) {
        if (l1 == null) {
            return l2;
        }
        else if (l2 == null) {
            return l1;
        }
        else if (l1.val < l2.val) {
            l1.next = mergeTwoLists(l1.next, l2);
            return l1;
        }
        else {
            l2.next = mergeTwoLists(l1, l2.next);
            return l2;
        }
    }

}
